Photos

There are many possible reasons, so we need to know some details, before we can help.

• What happened, before you no longer could open the library?Did you move, the library to a new location? Restore it from a backup? Install a software update? Run any cleaning applications tom remove duplicates?

Common reasons for Photos not running:

• After a system upgrade you may reusing an outdated alias on the Desktop or in the Dock. Try to launch Photos by clicking the icon in the Applications folder. This will ensure, that you are using the correct version of Photos.
• The Photos Library may have been opened with a newer version of Photos, for example on a different Mac with a newer system version. Then you can no longer use it on aMac with an older system.
• The library may be stored on an incompatible volume. The library needs to be on volume with the file system format MacOS Extended (Journaled) or APFS. The volume must not have been used for Time Machine backups. The volume must have a wired connection, not be a NAS or syncing with a cloud service, like Dropbox.
• A library may become damaged beyond repair, if the drive is failing, if you have been using dangerous cleaning applications to remove duplicates, by putting it in a synced folder, or by repeated crashes. Then restore a working version of the library from your backup.
• The library may contain legacy media, imported while using older system versions, that now can o longer be processed by Photos at all. Such items should have been removed while still running macOS 14 Mojave.

Could any of these apply?

As a test, try to launch Photos on a new , empty library. Is Photos working at all on a new library?